The present invention relates to a novel chlorine-free modified polyolefin composition with excellent adherence to nonpolar sheets, films and moldings of polypropylene, polyethylene, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, ethylene-vinyl acetate copolymer, etc., with excellent solvent resistance, oil resistance and weather resistance, with no tack, and also with excellent cohesion.
Because of low price, and many excellent properties such as moldability, chemical resistance, water resistance and electrical characteristics, polyolefins such as polypropylene and polyethylene are used widely in recent years as sheets, films, moldings, etc. Different from polar substrates such as polyurethane resin, polyamide resin, acrylic resin and polyester resin, however, polyolefin substrates are nonpolar and crystalline, leading to drawbacks of difficult paintability and adhesion.
So far, modified polyolefins obtainable by modifying polyolefins with unsaturated carboxylic acid and/or acid anhydride, and further acid-modified chlorinated polyolefins obtainable by chlorinating them have been used as paint additives, primers and adhesives, because of excellent adherence to said nonpolar substrates.
However, conventional acid-modified polyolefins represented by maleic anhydride-modified polyolefins have drawbacks of poorer adherence to non-polar substrates, more liability to cause cohesive failure, stronger tackiness, etc. compared with chlorination type modified polyolefins. Moreover, even chlorinated polyolefins with excellent adherence also have drawbacks of poor weather resistance etc. and, in addition, from recent upsurge of environmental problems, their uses have also become to be restricted. Based on such background, the development of novel chlorine-free resin with adherence to nonpolar substrates equal to or more than that of chlorinated polyolefin, and also with excellent physical properties such as tackiness and cohesion has been expected.
As one of the reasons why maleic anhydride-modified polyolefin is in short of physical properties, low activity of maleic anhydride on radical polymerization can be mentioned. In order to use maleic anhydride-modified polyolefin for the uses of adhesives, primers, paint additives, etc. for nonpolar substrates, at which the invention aims, it is required to graft a considerable quantity of maleic anhydrides onto polyolefin. However, because of low grafting rate by usual modification method, necessary physical properties cannot be obtained. If employing severe conditions in attempt to raise the grafting rate, then remarkable decrease in molecular weight results, leading to decreased physical properties. In the uses of compatibilizers, moldings, adhesives, etc., such techniques for obtaining modified polyolefin with high molecular weight and high grafting rate that use of maleic anhydride and styrenic monomer in combination are known, and, for example, U.S. Pat. No. 3,708,555, Japanese Unexamined Patent Publication Nos. Hei 1-221475, Hei 8-3415, 48873, 208907, Hei 10-36456, 306269, etc. are exemplified, including the literatures described in G. Moad: Prog. Polym. Sci., 24, 81 (1999). With these techniques, styrenic monomer equal to or more quantity than maleic anhydride is used. Moreover, in U.S. Pat. No. 5,021,510, Japanese Unexamined Patent Publication Nos. Hei 3-227341, Hei 4-46946, Hei 6-122738, Hei 9-40724, etc., the ratio of maleic anhydride to styrenic monomer is not particularly described, or the techniques cover very broad range.
However, in the uses, at which the invention aims, these conventional techniques could not be utilized from the facts that the solvent resistance, oil resistance and weather resistance decreased remarkably because of a large quantity of styrenic components contained. Moreover, in the case of low content of propylene in raw material polyolefin or in the case of high content of styrenic component in modified polyolefin, the adherence to nonpolar substrates decreased, which made it impossible similarly to utilize for those uses.
The purpose of the invention lies in providing a novel chlorine-free modified polyolefin with excellent adherence to polyolefinic resin moldings, with excellent solvent resistance, oil resistance and weather resistance, with no tack, and also with excellent cohesion.
As a result of diligent investigations for solving this subject, the inventors have found that, by using particular polyolefin for raw material and further using particular quantities of maleic anhydride and styrenic monomer for graft polymerization, thus by controlling the structure and molecular weight of modified product, the adherence to nonpolar substrates, solvent resistance, oil resistance, weather resistance, elimination of tack and enhancement of cohesion, etc. can be achieved at the same time, leading to the invention based on this knowledge.
As described, according to the invention, following (1) through (9) are provided.
(1) A modified polyolefin composition having the weight average molecular weight of not less than 30,000 to not more than 150,000, obtainable by graft polymerizing 0.5 to 15.0% (by weight) of (B) maleic anhydride and 0.1 to 7.5% (by weight)of (C) styrenic monomer to (A) polypropylene, ethylene-propylene copolymer or ethylene-propylene-butene copolymer, so as the grafting weight ratio (B/C) of (B) to (C) to become not less than 2 to not more than 5.
(2) The modified polyolefin composition described in (1), wherein the composition ratio of propylene in (A) polypropylene, ethylenepropylene copolymer or ethylene-propylene-butenecopolymer described is not less than 50%.
(3) A modified polyolefin composition obtainable by graft polymerizing (B) maleic anhydride and (C) styrenic monomer onto polyolefin, characterized by said polyolefin being (A) polypropylene, ethylene-propylene copolymer or ethylene-propylene-butene copolymer, the grafting rates of (B) to (A) being 0.5 to 15.0% (by weight) and of (C) to (A) being 0.1 to 7.5% (by weight), the weight ratio (B/C) of grafting rate of (B) to the grafting rate of (C) being not less than 2 to not more than 5, and the weight average molecular weight of the graft polymer grafted (B) and (C) onto (A) being not less than 30,000 to not more than 150,000.
(4) The modified polyolefin composition described in (3), wherein the composition ratio of propylene (by weight) in (A) polypropylene, ethylene-propylene copolymer or ethylene-propylene-butene copolymer is not less than 50%.
(5) The modified polyolefin composition described in (3) or (4), wherein it is a chlorine-free modified polyolefin composition.
(6) An adhesive using the modified polyolefin composition of (1) through (5).
(7) A primer using the modified polyolefin composition of (1) through (5).
(8) A paint binder using the modified polyolefin composition of (1) through (5).
(9) An ink binder using the modified polyolefin composition of (1) through (5).
The nonpolar substrates referred to so in the invention point to nonpolar sheets, films or moldings of polypropylene, polyethylene, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, ethylene-vinyl acetate copolymer, etc. Also, they include surface-treated ones of these substrates with plasma, corona or the like.
The polyolefins that become the raw material of modified polyolefin to be used in the invention are polypropylene, ethylene-propylene copolymer and ethylene-propylene-butene copolymer.
The composition ratio of propylene in the polyolefins that become the raw material of modified polyolefin is preferable to be not less than 50%, more preferably not less than 60% to not more than 98%. If under 50%, then the adherence to propylene and polyolefin substrates is poor.
The usable molecular weight of polyolefin can be selected freely so as the weight average molecular weight of modified polyolefin to become 30,000 to 150,000, but, even a polyolefin with weight average molecular weight of over 150,000 becomes usable by the publicly known methods for adjusting the molecular weight to a suitable range by degrading in the presence of heat or radical, and others.
As the styrenic monomer to be used in the invention, styrene is used most preferably, but unsaturated aromatic monomers such as o-,p-, xcex1-methylstyrene and divinylbenzene can also be used.
In the invention, it is required to graft maleic anhyride and styrenic monomer in amounts of 0.5 to 15.0% and 0.1 to 7.5%, respectively, to the weight of raw material polyolefin. In addition, it is required to control the ratio of grafting weight of maleic anhyride to grafting weight of styrenic monomer so as to become not less than 2 to not more than 5. If the grafting weight of maleic anhyride is under 0.5% , then the solubility into solvent and the compatibility with other resins are poor, and, if over 15.0%, then a large quantity of maleic anhyrides are used, resulting in the generation of much residual monomer, which is unpreferable. If the grafting weight of styrenic monomer is under 0.1%, then effect of suppressing the drop of molecular weight and effect of increasing the grafting rate of maleic anhyride cannot be obtained, thus generating much residual maleic anhyride monomer. If over 7.5%, then the solvent resistance, oil resistance and weather resistance decrease remarkably or the adherence decreases, which is unpreferable. Similarly, with regard to the ratio of grafting weight of maleic anhyride to grafting weight of styrenic monomer, too, if it is over 5, then effect of suppressing the drop of molecular weight and effect of increasing the grafting rate of maleic anhyride cannot be obtained, thus generating much residual maleic anhyride monomer, and, if under 2, then the solvent resistance, oil resistance and weather resistance decrease remarkably or the adherence decreases, which is unpreferable.
In the invention, the grafting reaction can be performed irrespective of the presence of radical initiator, but it is more preferable to use the initiator, and use of organic peroxides, for example, benzoyl peroxide, dicumyl peroxide, lauroyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, etc. is preferable. The type and the use level of radical initiator can be selected appropriately depending on the reaction conditions, but it is desirable to use around 0.1 to 5 wt. %. If under this level, then the grafting reaction rate decreases, and, even if over that, the drop of grafting reaction rate and the side reactions like internal crosslinking and decreasing of molecular weight can result.
The grafting reaction of maleic anhyride and styrenic monomer onto polyolefin raw material is possible to perform by publicly known methods, for example, the solution method wherein raw material polyolefin is dissolved into solvent such as toluene, to which radical initiator, maleic anhyride and styrenic monomer are added, and the melt method wherein, employing Banbury mixer, kneader, extruder, etc., radical initiator, maleic anhyride and styrenic monomer are added to molten raw material polyolefin, and the like are mentioned. The order, method, etc. of adding maleic anhyride, styrenic monomer and radical initiator can be selected appropriately. Moreover, it is also possible to remove residual monomers by providing a pressure-reducing process at the time of completion of reaction.
The weight average molecular weight of modified polyolefin obtained is 30,000 to 150,000, preferably 30,000 to 120,000. If under 30,000, then the adherence to nonpolar substrates and the cohesion are poor, and, if over 150,000, the workability and the solubility into solvent decrease due to the increase of viscosity.
The weight average molecular weight of modified polyolefin can be determined by means of GPC (gel permeation chromatography) etc. Moreover, the grafting rate of maleic anhyride and styrenic monomer can be measured by extracting them using MEK, acetone, MEK-methanol mixed solvent, or the like, and then by using titration, FT-IR, NMR, etc.
The inventive modified polyolefin can be used as an adhesive, primer, paint binder resin and ink binder resin for nonpolar substrates. It can be used in the forms adapted to uses such as solution,powder and sheet. Moreover, if needed, additives, for example, antioxidant, light stabilizer, ultraviolet absorber, pigment, dye, inorganic filler, etc. may also be formulated for use. Moreover, based on the fact that the inventive modified polyolefin is excellent also in the compatibility with other resins, other resins such as urethane resin, epoxy resin, acrylic resin, phenol resin, alkyd resin, silicone resin and nitrocellulose may be blended additionally when using as a binder for paint or ink, if further needed.